The effects of salts were investigated on thermo-coagulation of bovine serum albumin (BSA). Salts affected the formation of coagulum, and a “minimum” (a col) on the turbidity-pH curve was observed at about pH 7.5. When the time course of turbidity was measured at more acidic pH (6.5) or alkaline pH (9.5), an induction period was observed at the more alkaline pH (9.5). The turbidity- pH curve for carboxyamidomethylated BSA was similar to that of original BSA. When salts were added to reduced, carboxyamidomethylated BSA solution, no “minimum” appeared on the turbidity-pH curve. The amount of free sulfhydryl groups, either in the presence or absence of salts, increased with heating time at more alkaline pH (pH 9.5). Intermolecular protein interactions occurred easily when salts were present. The endothermic peak on differential scanning calorimetry thermograms did not appear when salts were absent, but appeared when they were present.